Method of forming a storage electrode



March 1', 1960 F. H. HARRIS METHOD OF FORMING A STORAGE ELECTRODEOriginalFiled llay 1, 1957 3 Sheets-Sheet 1 j a m w. .v m s m E l O v.n+ MM w A .A 5 mm H 5 09 mm m L F. mm o ov K 8 Wm M 6 09 F I we C Y 35+omm+ v m B NN O March I 1 960 js 2,926,419

METHOD OF FORMING A STORAGE ELECTRODE Original Filed llay 1, 1957 3Sheets-Sheet 2 &. am mm w: a ssmm 1 w msxwmsamsss INVENTOR FRANKLIN H.HARRIS i ATTORNEY) shown by illustration inv Fig. 1 comprises anevacuated glass" envelope 11 which encloses a storage electrode ormosaic 12 and two conventional cathode-ray guns 13 and .14. The cathoderay guns-are positioned respec tively in opposite ends of the tube onopposite sides of the storage electrode and are magnetically focused anddeflected in the conventional manner as used in television picturetubes. Conductive coatings 15 and 16 of silver paint are respectivelyprovided on the inside and the outside of each end of the envelope toshield the storage mosaic from the electrostatic fields of thedeflection coil and yet does not interfere with the magnetic fields. Theinner coatings 15 merge with transparent conductive coatings 17, such asa metallic oxide, which serves as the second anodes. and are transparentto facilitate'inspection of 'the inside of the tube if desired. Acylinder 18 positioned within the envelope on the readbeam side of thestorage mosaic serves to collimate the read-beam electrons in order toobtain equal values of forward electron velocity over the surface of themosaic. The collimating cylinder is provided with a ridge 19 about theouter surface thereof for the purpose of securing the cylinder Withinthe envelope; for purpose of illustration, three glass holders 21 areprovided for securing the collimating cylinder in position. The innersurface of the collimating cylinder has three equally spaced t'abs orlugs 22 attached thereto along one end about the inner circumference toprovide means for securing the mosaic surface in position with respectto the electron guns and the collimating cylinder. The tube is providedwith a getter 27 to keep the residual gas pressure low during operation.

Fig. 2 illustrates the relationship of the collimating cylinder and themosaic surface. The mosaic surface is formed between two hoops or rings23 and 24, one fitted into the other to hold the mosaic surfacetherebetween and then assembled between a metal disc 25 through whichelectrical connections are made to the metal screen of the storagesurface and mica disc 26 made of several layers of mica by three bolts28 and nuts 29. Any suitable insulators 31 such as glass, are providedto insulate the metal disc from the bolts and also to provide spacebetween the metal disc 25 and mica disc 26 in which space the mosaic ispositioned. Mica disc 26 has a metal disc 32 secured thereto by tabs 33which are bent over along the surfaces of the metal disc 32 andconnected to a few of the mica layers of the'mica disc 26. Metal disc 32is cut away in the vicinity of the bolts 28 and therefore does not haveto be insulated therefrom. The ends of bolts 28 are insertedthrough lugs22 and connected thereto by nuts 34 and the mica disc and the metal disc25 is connected to thebolts by nuts 29 screwed on the ends of the bolt,the collimating cylinder and mosaic surface is now ready for assembly inthe envelope and connected to the proper lead lines from suitable pinsin the connector 30. I

The mosaic is made of a very thin metal screen 35 having a thicknessfrom about 0.00005 to 0.0006 inch and with from about 300 to 1000 meshper inch. The thin metal screen is covered with bentonite clay by amethod to be described later to form a very, very thin dielectricsurface 36 which fills the openings or interstices of the screens andalso covers the screen surfaces,

however, that portion of the dielectric which covers the screen surfaceis much thinner than that which fills the openings and the dielectriceffect of that covering the screen is negligible since it is so thin;therefore, in effect, the dielectric film in each of the intersticesform individual isolated cells separated by the conducting portions ofthe screen. The mosaic is secured to the collimating cylinder andpreferably positioned to receive the write beam on the dielectric sideof the wire screen.

Fig. 3 is a schematic of the tube illustrating the operating voltagesfor the various elements and in operation of an assembled tube, magneticfocusing and electron acceleration is carried out by conventionaltelevision type scan circuits 37 illustrated in block form by Fig. 4 inwhich the accelerating and focusing assemblies are maintained at apositive potential with respect to ground. The write cathode 41 ismaintained at an operating negative voltage of about 1000 volts by anysuitable grounded voltage source not shown and has connected thereto avariable write beam current control 42 of volts for controlling theperiod during which writing proceeds. Electrons emitted by the cathodeare resolved in the usual mannerv by the accelerating and focusingmechanism into a-writing beam of small cross sectional diameter and highintensity, the intensity of which may be modulated by informationsignals originating with an information signal source 43 and impressedupon the write control grid 44 in the form of v,varying voltages. Thebias of the control grid relative to thecathode may be adjusted asdesired by a variable tap 45 on the current control 42and has adecoupling resistor 46 connected between the grid and the tap. The firstanode 47 is placed at a relatively high potential such as positive 1.5kvcwith respect to the cathode and a second anode 48 is placed at apotential still higher than the first anode such as a positive 3 kv.with respect to the cathode. The second anode is the same as the innercoating 17 and has an additional purposeof collecting secondaryelectrons which escape from the mosaic. Between the first anode and thewrite grid a second grid 49 with a negative voltage of about 500 voltsis placed. The electrons from the write gun strike the insulation withsufficient energy to generate secondary electrons in excess of theprimary electrons on the insulator. The mosaic is maintained at zeropotential and is brought out through an external load resistor 51 toground. The video output from the mosaic is taken off by a terminalbetween the resistor and the mosaic and connected to the input circuitof a video amplifier 52 which is then connected to the control grid of amonitoring cathode-ray picture tube 53. 1

The read beam and holding electron gun assembly 13 islocated on theopposite side of the mosaic from thewrite gun 14 and focuses the readbeam current onto the metallic screen and insulator cells of the storagemesh with a constant beam current. The read cathode 54 has a negativepotential of about 40 volts for holding without any decay. The cathodehas connected thereto a read beam current control 55 which is connectedto a control grid 56 by a variable tap 57. A second control grid 58having a positive potential of 400 volts relative to the cathode ispositioned about the cathode between control grid 56 and a first anode61 which has a positive potential of 1.5 kv. with respect to thecathode. Asecond anode connection 62 connects with the inner coating 15and the transparent coating which forms the second and has an additionalpurpose of collecting stray electrons and to help protect the mosaicfrom electrostatic forces. Collimating cylinder 18 having a positivepotential of 350 v. is positioned on the read beam side of the tubeadjacent to mosaic 12 and serves to collimate at right angles the readbeam electrons with respect to the mosaic surface. Metal disc 32connected to the mica plate 27 is electrically connected to an outsideterminal and adapted to be provided with a positive potential, ifadditional electron correcting features are required for collimation. I

In the preferred operation of the device, the insulatorcells of themosaic are erased and prepared for writing by priming to the black" bymeans of a priming cycle. This is done by scanning the insulator-cellswith a read beam whose cathode voltage is nearly at zero, then in ashort time about second, the cathode voltage is re I tra nee-n You thesurface of the envelope.- i g v V I In reading the stored signal, theelectronsfrom the insnlator -ce s.

fead eathode voltage, and th-us iriainta I u trons, ebnsequently, veryfew secondary electrons are released-by the surface. The efiectofprimingthe mosaic is' to cause negative charges to appear on the writeside a w velocity of arriving read else-- [write electrons with 1000volt's energy strikes the in= of the-insulator wherein during theWriting period, electrons with; about 1000 volts} energy strike theinsulator Wit ample velocity to" genefate'secondary electron'sin excesof; the primary-electrons from the ;Write-:cathode.

The escaping secondary electrbns in excess of the numberet beamelectrons striking-the insulator results in a net;positive charging ofthe insulator and results in writing on the mosaic. The escapinsecondary electrons are collected by. the positive co-ating'of thesecendanode readelectron gun 13 providing 'the read beam are fo'rentfrom thei'conductive metallic mesh, owing to charges in theinsulatorlcells; register as" variations in the current 'throughtheloadresistor 51-;corinected externally to. the eionduc't' emesh andconstitute the output-reading current. The load resistor "51 hasnegligible D.C.

voltagefdroplas a consequence of the read or wr'ite'b'eam curr" ts.'Simultaneous with reading, the read beam re% The variations in secondaryescape curreturn to their normal temperatures whereby the screengenerates original Written charges within-Z each insulator" c'ell by'its holding "action. {The bombarding velocity has the same value of allparts of the mosaic because the =deflection'angles" are cancelled out bythe lens produced by the col-liniating cylinder. At read-beamfbombarding energies less than thecritical potential; V (thep'otentialofthe bombardeddielectric portionwith respect to V theelectron source, where the total number of'secondary "electronses'caping from the surface of the dielectric equals the totalfnurnber ofprimary electrons absorbed by it) the insulator-"cells accumulateelectronsand charge negatively to a potential Y At'read-beam bombardingenergies higher than V the insulator cells lose electrons and chargepositively to an equilibrium potential V where the potential of theinsulator cells equals the po tential of'the conducting member. Theholding action ofthefread-beam overcomes electrical leakage and otherdeleterious effects, and thus the charge pattern established by the,writebeam is maintained withirfeach storage cell v at either thepositive equilibrium potential V (white) or the negative equilibriumpotential V tblack),

Airnore complete and detailed discussion of the elec-'tri'cal-;-operation of tlie r'nosaic due to the incident beam from theWriting and reading guns is set .forth in my copending applicationSerial No. 288,365, filed May 16,

It is to be understood that the new mosaic of the present invention can"be used with a three gun tubewherein fthe read and write guns are onvoppositetsides of the :mosaic and the holding gun isset oii to one sideon-the read side of the mosaic. The operation of the holding gun issubstantially the sameas described in my re ferred to copendingapplication andthe holding beam is properly focused onto the mosaic by,the .collirnating cylinder.

"In operation of the two gun s'torage 'tube for'long time storage themosaic isrprimed to charge the insulator cells ne'ga'tivelyiin order tomaintain low velocity of arriving flp'laced with the 2.8Xl0- partssolidf -'bentonite ela y read electrons, during priming negative chargesare caused to appear" on the {write side-sot the insulator;

sulator with "am le velocity to generate s'econdaryelec trons in excessof the primary electrons. The excessj I secondary electrons escapeto'result in"- a net positive charge on the insulator which correspondsto writing white. The net positive charge remains on the" insulator.s'urface, then the read beam of a negative 40' volts is focused on-theread side of the screen. The read beam scans'the metallic screen andinsulator cells of the storage surface to provide'secondary electrons.Due to: the charge of the. screen and, insulator; the secondaries areemitted with very low velocities and are easily controlled by the nearbyelectric fields of the insulator cellstThe, variationin secondary escapecurrent, from the metallic screen mesh due to the charges in'theinsulator cells, register as variations in the current through the loadre: sistor connected to the screen mesh and constitute the output signal(reading current) to'the cathode ray tube circuitry where the signal isreproduced on the screen of the'cathode raytube. i

The mosaic comprisesathin dielectric film h ving a thickness of fromabout 102 micron to about 1.3 mi;

crons' which bridge the openings of a fine mesh nickel screen having athickness of about 0.00005 to about 0.0005 inch and fro-m 300 to 1000meshfper inch-and formed according to' the following method; The -screenis -placed over a nickel-plated steel ring OIfhOOp 23,

stretchedtaut and then held in position by placing ring 23 into a secondlike ring 24 of larger diameterr ln orderto positionring 23 withthe'fine mesh over it. into ring 24, ring 23 is cooled to shrink thering and ring 24 is heated to expand it. The screen covered .r'-in'g isilleli slidQiZlitQ 'ring24 and thering's are allowed to and ring is heldtightly in ring 24. The assembly is then cleaned by Washing it in waterwith a detergent and then'in acetonejto remove any foreign solids, saltsor oils. LThen the assembly is placed on a level surface and water isapplied to the screen surface for wetting purposes.

The dielectric film is formed from a preparatio-n of vbentonite clayhydrosol made from bentonite clay (montmorillonite) which is a naturalmineral classed as an 'alurninosilicate Al (Si O ).xH O. A refined formof bentonite clay hydrosol containing 2.3% solids by weight is dilutedwith distilled Water to form a'fluid which contains a much lowerconcentration of solids about 2r8 l0f parts by weight In percentageconcentrations of 1% or more, the hydrosol has the property of being athixotropic gel (the property of becomingfliiid when agitated andreturning to a gel when left undisturbed). '1l1e"dilute'2.8 10-' partssolid hydrosol appears to have the properties of viscosity and surfaceten sion identical to those of distilled water and can be applied to thescreen in liquid form. I s s The screen is prepared for coating asdescribed above and the surface thereof wet: with a pool of distilledwater one to two millimeters deep for approximately twenty minutes.The'small meshof the screen and the-surface tension of the waterserves-to prevent the water from going through the screen; howevenif thescreen'is extremely clean the Water will run through. In. order toobviate this, the screen is purposelycontaminated with any suitablesolution, for example by immersing the screenmomentarily in a solutionof amyl acetate and 10* parts by volume of co'llodion. Thisis allowed '0dry and then the distiiled'water is placed onthe surfaee as describedabove. c

After the distilled water has been on the screen surface approximately20 rninutes,.most of the water is drained ofi'with the aid of anaspirator or any other convenient means. The removed .distilled waterimmediately rehydrosol which has been vigorously stirred to-insnreathorough dispersal of the solids. Approximatelytfour evaporates from thesolution and the surface of the screen, to leave a uniform film ofbentonite clay which weighs approximately 1.1 milligrams and having athickness of 0.1 micron (4X inches). The average thickness of the filmis determined by the formula where d is the thickness in microns, w isthe weight in grams of the formed film, S.G. the specific gravity, and Ais the area- (cm?) of the covered screen. The above values for formingthe dielectric film are typical values for a preferred dielectric filmand other concentration of solids may be used to form films havingdifferent thickness. Hydrosols containing 8.25 1O' to 2.0 1O- solidsby-weight will form suitable dielectric films having a thickness of fromabout 0.02 micron to about 1.3 microns, the thickness of the dielectricfilm is limited by the thickness and strength of the screen surface. Ifthe hydrosol placed on the screen is too heavythe screen will tear awayand films cannot be formed; therefore, the thickness of the film islimited to the strength of the screen. 4 7

It is highly important that dust particles do not settle on the screenduring forming and that the film have uniform thickness. For thispurpose the screen is placed on a stationary level stand or fiat surfaceand a glass cover is placed over the screen as soon as the hydrosol hasbeen placed on it. Since the screen is covered, drying proceeds slowlywherein the water is forced to evaporate primarily from the undersidethrough the openings in the screenf Since the hydrosol has approximatelythe properties of viscosity and surface tension of distilled water, thefluid is pulled by gravity into the interstices of the screen whereinthe fluid clings to the screen surface due to surface tension, thisforms a uniform film within the interstices which is thicker than thefilm over the screen surface. When the water has evaporated and the filmformed onto the screen, the screen is removed from the. glass cover. Thescreen in this state can be used as a storage surface; however, the filmdoes not demonstrate as low an electrical conductivity as mica and hasslight electrical leakage, therefore it is necessary to further treatthe film to obtain the desired dielectric qualities.

The bentonite clay film can-be converted to a lowconductivity materialsimilar. to mica by either of the following two methods. In one method,the storage screen is removed from under the glass cover and placed in acontainer such as a stainless steel vented container and heated atapproximately 1000 degrees for minutes in hydrogen. The stainless steelvented container serves to shield the screen from the heating flame ofthe hydrogen furnace and'also provides thermal lag which preventsrupture of the storage surface when the container is removed from thefurnace. The screen being thin would shrink more rapidly than themounting rings and therefore would rupture if allowed to cool toorapidly. The storage surface is removed from the hydrogen atmospherewhile it is hot (approximately 400 degrees Centigrade) and cooled withinthe container in air. It has been determined that removal from thehydrogen at a temperature below 400 degrees centigrade makes thebentonite film slightly conductive and when removed at temperaturesgreater than 400 degrees centigrade, a slight oxidation of the nickelscreen occurs. Oxidation is not significantly harmful for operation inthe tube of the present invention.

1 In another method of converting the bentonite .clay .film to alow-conductivity material, the film is treated with lead. Bentonite claydispersed in water is necessarily sodium bentonite, therefore the driedfilm on the sereenis sodium bentonite clay. The assembly of the 8 screenwith the dried film thereon isimrnersed in a concentrated lead-nitratesolution. A base exchange reaction occurs inwhich the sodium of the filmis replaced by lead. 'After about a five minute immersion in thelead-nitrate solution, the assembly is removed from the solution, rinsedwith distilled water and then dried. The films are nonconductive andhave the properties of mica. Films as thin as 20 millimicrons have beenformed by this method, wherein such thin films formed by the firstmethod would disintegrate due to the high heat intensity.

In either method described above, the conductivity of the films iscomparable to that of mica, and this, combined with their thinnessresults in negligible conductance along their plane. Even though thefilms are verythin, they can withstand the high bake temperature (400C.) required to outgas the tube. In addition sodium-bentonite films haveexcellent mechanical adherence to the nickel screens in order to formthe thin films in the interstices of the screen and in which thatportion of the film cover.- ing the conducting portions of the screenare thinner than that within the interstices.

A mosaic formed according to the above method combines a metal screenand a very thin insulator in which the insulator is formed in theinterstices such that the cells of the insulator are electricallyguarded one from the other by the conductor screen. The read beambombards both the conductor and insulator to fulfill read and holdfunctions, and the write beam can. charge the insulator and control thefield on the read side. The latter is attained by forming the insulatorvery thin, so that large voltages cannot exist between the write andread'surfaces, and the insulator has high resistivity so that thewritten charges will not leak ofi.

In some other type cathode ray tubes it may be desirable to make aconductivescreen with a thicker insulator surface in which it isessential that one face surface of the screen be in contact with theinsulator material. For such tubes, the storage electrode made accordingto the above method can be used wherein the dielectric film side of thestorage electrode is used as a substrate and an insulating materialadded thereto by any well known method such as the evaporationtechnique, or the water dispersed colloid suspension method. For examplequartz, silicon dioxide or aluminum oxide can be added to the bentoniteclay film to increase the thickness of the insulating surface. Theapplication of the additional insulating surface by the colloidsuspension method is preferred since the liquid would fiow into theinterstices fill the interstices and then provide a smooth outersurface. In the evaporation method the insulation would buildup over thescreen surface as well as in the interstices. The method used depends onthe outer surface desired.

The present invention is concerned with the use of this dielectric filmfor the mosaic of a storage tube, however, it would be obvious to anyoneskilled in the art to use thin dielectric films for other uses;therefore, it is to be understood, that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed. 1

What is claimed is:

l. The method of making a storage electrode for a signal devicecomprising a grid-like structure having a plurality of intersticestherein mounting said grid-like structure under slight tension betweenthe outer and inner surfaces of two loops, cleansing said structure toremove foreign solids, salts and oils, placing said structure on a levelsurface, wetting said grid-like structure with a deepness of from aboutone to two millimeters of distilled water, draining the major portion ofsaid distilled water from said surface, replacing said water withsufficient fluid bentonite clay hydrosol to cover said grid-likestructure and allowing said liquid to dry slowly to form a film ofbentonite clay over the surface of said grid-like structure and acrossand into said plurality of interstices in a 9 plane midway between theouter surfaces of said grid like structure.

2. The method of making a 'storage electrode for a signal storage devicecomprising a grid-like structure having a plurality of intersticestherein, mounting said gridlike structure under slight tension betweenthe outer surface of one hoop and the inner surface of a second loop,

cleansing said structure to remove foreign solids, salts and oils,placing said structure on a level surface, wetting said grid likestructure with a'deepness of from about one to twomillimeters ofdistilled water for about 20 minutes, draining the major portion of saiddistilledwater from said surface, replacing said water with sufficientfluid bentonite clay hydrosol to cover said grid-like structure with apool one millimeter deep, allowing said liquid'to dryslowly to form afilm of bentoniteclay over thefsurplurality of interstices in a plane:midway between the outer surfaces of said grid-like structure. 7

3. The me'thodas claimed in claim 2 wherein a cover is placed over thegrid-like structure. during drying to prevent dust particles fromfalling thereon. q

4. The method of making a storage electrode for a signal storage devicecomprising a nickel grid like struc ture having a plurality ofinterstices therein, mounting saidgrid-like'structureunder slighttension between the outer surface of one nickel-plated steel hoop andthe inner surface of a second nickel-plated steel hoop, cleansing saidstructure by washing .first in water with a detergent, then in acetone,to remove any foreign'so lids, salts and oils, contaminating saidgrid-like structure by immersing it momentarily in a suitablesolution,placing said struc- 'ture on a level surface, wetting said grid-likestructure by covering the surface rwith' a pool of distilled water oneto two millimetersdee'p for about '20 minutes; draining said distilledwater fromfthe surface of said structure, replacing said distilled waterwith a one millimeter deep pool of liquid bentonite clay hydr osol overtheentire surface, covering the structure and allowing the liquid toevaporate to form a film of bentonite clay on one surface of saidgridlike structure and into and across said interstices in ,a

' plane midway between the outer surfaces of said grid-like" structure.

5. The method of making a storage electrode for a signal storage devicecomprising-a nickel grid' 'like structure having a plurality ofinterstices therein, mounting 'face" of said grid-like structure andacross and into said nitrate solution for approximately five minutes,removing said grid-like structure under slight'tension between the outersurface of one nickel-plated steel hoop end the, in-

ner surface of a second nickel-plated steel hoop, cleansing saidstructure by Washing first in water with a detergent,

then in acetone, to remove any foreign solids, salts and oils,contaminating said grid-like structure by immersing it momentarily in asuitable solution of amyl acetate and about 10 parts by volume ofcollodion, allowing said contaminated structure to dry, placing saidstructure on .a level surface, wetting said grid-like structure bycovering the surface with a pool of distilled water one'to twomillimeters deep for about 20 minutes, draining said distilled waterfrom the surface of said structure, replacing said distilled water withaone millimeter deep pool'of liquid bentonitefclay'hydrosol over theentire surface, covering the structure and allowing the liquid torevapo-7 rate to form a film of bentonite clay on one surface of saidgrid-likestructure and into andracross saidtinterstices in a planemidway between the outer surfaces of I said grid-like structure. I V t V6. The method as claimed in claim 4 wherein the formed film is furthertreated to form a low-conductivity insulator material. v

7. The method as claimed in claim 4 wherein the formed film is treatedto form a low-conductivity insu- -lator material by placing saidstructure in a container and firing the storage structure at about 1000C. for about 20rninutes in hydrogen, allowing the surface to cool downto approximately 400 C., removing the container from the hydrogenatmosphere and allowing said structure to cool within said container inair.

8. The method as claimed in claim 4 wherein the film is treated to forma low-conductivity insulator material by immersing the'storage structurein a concentrated leadthe structure from said lead-nitrate solution,rinsing in distilled waterand allowing the storage, structure to dry.

T References Cited in the file of this patent UNITED STATES PATENTS

